Postgresql monitoring question

I inherited a postgresql database which has queries run against it
from perl scripts.  I need to determine which query from the scripts
is taking an extremely long time, but do not know how to monitor or
identify queries as they are run against the database.

I know little of postgresql, but quite a bit about SQL and databases
in general.

Are there tools I can use to monitor or log (*not* transaction log)
what is going on inside the database.  Once I can identify the query,
I can go into the perl code (several thousand lines) and figure out
the part I need to modify (assuming that I need to change the perl),
or which tables/indexes to optimize.

Thanks for any help.